A light-detection technique may count individual photons to measure intensity of light (e.g., a single photon counting (SPC) technique). For example, incident photons may be counted individually over a period of time to obtain a measure of light intensity and/or flux during an imaging operation.
A circuit to implement the light-detection technique may be complex. The complexity of the circuit may reduce image resolution because of a lower fill factor and/or an increased pixel size. The increased pixel size may prevent a use of the circuit as arrays.
A delay (e.g., a dead-time) may be created after a photon is received until a circuit (e.g., a light-detection circuit) is ready to receive another photon. A reduction of the delay may be prevented because of an implementation of the circuit on a slow semiconductor technology. For example, a solid-state single photon counter that is integrated on a microchip may be implemented in a long channel technology that uses a semiconductor with a lower doping level. The reduction of the delay may also be prevented because of an afterpulse caused by a trapped carrier being released. The afterpulse may be counted as incident photons leading to an inaccuracy in a photon count. As a result, the delay may limit an upper photon count rate, making the light-detection technique unsuitable in an application (e.g., a biomedical application, a military application, a nighttime imaging operation, a low light imaging operation) requiring high-speed processing during the imaging operation.
In some applications, such as satellite imaging, an image sensor device may utilize time-delay integration (TDI) to increase sensitivity due to low light conditions or due to objects moving at high speeds. As such, the image sensor device may require a short integration time to avoid blurring of the image. Conventional TDI systems may use charge-coupled devices to facilitate charge transfer, which is required in TDI to shift a charge from one pixel to another in a manner synchronized with the movement of an object being captured by the image sensor device.
However, the large amount of circuitry in conventional CCDs of current image sensor devices may limit a resolution of the image sensor device. For applications such as satellite imaging, a low resolution image may degrade the overall appearance of the image and may cause certain infinitesimal features, such as stars, to be obscured. Furthermore, to facilitate TDI, a high bandwidth operation amplifier may be required to enable and maintain high speed operation. However, the inclusion of an operation amplifier would further limit the layout area of the circuitry. Also, analog solutions may require an additional analog to digital conversion process as in conventional CCD-based TDI imagers.